Field
The present application relates to methods and apparatus for characterizing the solubility of asphaltenes of a hydrocarbon fluid sample.
Related Art
Solubility analysis is used in the petroleum industry as a guideline to evaluate the stability and compatibility of the oil constituents of a reservoir fluid sample, often when the sample is mixed with diluents or when comingled with other oil mixtures as described in Nikooyeh, K. and Shaw, J. M., “On the Applicability of the Regular Solution Theory to Asphaltene and Diluent Mixtures,” Energy & Fuels, Vol. 26(1), 2011, pp. 576-585 and in Wiehe, I. A., “Process Chemistry of Petroleum Macromolecules. Chemical Industries”, Taylor & Francis, 2008. The regular solution theory is commonly described as “like dissolves like” and states that two compounds with close solubility parameters are likely to be mutually miscible.
In particular, solubility analysis is used in the petroleum industry to study the asphaltene component of oil that can precipitate upon a change in pressure, temperature, or composition of the oil mixture; generally attributed to a variation in the solubility matrix. In fact, asphaltenes are typically defined as a solubility class of material, being poorly soluble in alkanes (e.g. n-heptane) and highly soluble in aromatic solvents (e.g. toluene). Asphaltene solubility parameters, calculated and/or measured, are used as inputs to many modeling approaches that predict asphaltene behavior when crude oils undergo physical and or chemical changes as described in Alboudwarej, H. et al., “Regular Solution Model for Asphaltene Precipitation from Bitumens and Solvents,” AIChE Journal, Vol. 49(11), 2003, pp. 2948-2956, and Hirschberg, A. et al., “Influence of Temperature and Pressure On Asphaltene Flocculation”, Society of Petroleum Engineers Journal, Vol. 24(3), 1984, pp. 283-293 and Andersen, S. I., and Speight, J. G., “Thermodynamic Models for Asphaltene Solubility and Precipitation”, Journal of Petroleum Science and Engineering 22, no. 1-3 (1999): pp. 53-66. The precipitation and deposition of asphaltenes from reservoir fluids during production, transportation, sample handling, and processing of reservoir fluids is a major impediment with associated costs on the order of billions worldwide as described in Rogel, E., Ovalles, C. and Moir, M., “Asphaltene Stability in Crude Oils and Petroleum Materials by Solubility Profile Analysis”, Energy & Fuels, Vol. 24(8), 2010, pp. 4369-4374. Optimal flow assurance requires that models accurately predict asphaltene behavior in order to identify and avoid problematic conditions. Therefore, consistent and reliable measurement techniques that report asphaltene solubility profiles are useful for managing these production problems.